The purpose of the variable capacity torque converter (Figure above) is to allow the operator to limit the amount of torque increase in the torque converter to reduce wheel spin and to divert power to the hydraulic system. The main components of the unit are the inner impeller, outer impeller, impeller clutch, turbine and stator. The inner impeller, turbine and stator all function essentially the same as in the conventional torque converter previously covered. The principal difference is that the impeller is split so there is an additional impeller for greater torque management flexibility.
The outer impeller (The figure above) is the second impeller within the torque converter. The outer impeller rotates with the converter housing when oil pressure acts on the clutch piston to engage the clutch pack. When maximum oil
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Hydraulic Coupling pressure fully engages the clutch, the outer impeller turns with the inner impeller. When there is a reduction of oil pressure, there is clutch slippage resulting in the outer impeller turning slower and a reduction of torque converter capacity.
The impeller clutch is hydraulically activated and controlled by the transmission hydraulic system. The clutch connects the outer impeller to the rotating housing allowing the inner and outer impellers to turn together.
Impeller Clutch Oil Flow
In the full power mode, oil pressure acts on the clutch piston which engages the impeller clutch and causes the outer impeller to turn with the inner impeller. With both impellers rotating at the speed of the housing, the impellers displace the full amount of oil and the torque converter produces maximum torque. When the clutch is completely engaged there is no clutch slippage allowing the torque converter to operate as a conventional torque converter. In the reduced power mode (The figure above, right diagram), oil pressure decreases at the clutch piston allowing the clutch to slip. The clutch transfers some of the power from the rotating housing to one impeller. One impeller rotates
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Hydraulic Coupling at the same speed as the rotating housing and one impeller rotates slower. The impellers do not displace the full amount of oil and torque converter output is reduced. At minimum capacity, the operation of the variable capacity torque converter is similar to a conventional torque converter, except that the effective size of the impeller has been reduced due to impeller clutch slippage. Impeller displacement depends on the speed of the impeller. Slower speed means less displacement and less displacement means less power transfer. The clutch slips in order to keep the wheels from slipping. The machine operator sets the amount of slip by varying the pressure behind the clutch piston.
Benefits of Variable Capacity Torque Converter Similar to the impeller clutch torque converter, the variable capacity torque converter keeps the wheels from slipping during bucket loading operations. The variable capacity torque converter also increases available engine power.